Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-03-20
2002-10-29
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S036600, C428S036700, C428S435000, C428S446000, C428S458000, C428S474400, C428S480000, C428S483000
Reexamination Certificate
active
06472035
ABSTRACT:
The present invention regards stretched polyester resin foamed sheets, which are heat-sealable, and suitable for the production of beverage and food containers, on which a design can be stamped from which, by folding, the shape of the container can be developed.
BACKGROUND OF THE INVENTION
The materials employed till now for the production of beverage and food containers such as containers for fruit juices, milk or otera include substantially a fictional layer of cardboard which gives the container mechanical properties, in particular rigidity, and, adhered to the cardboard, in some cases, a layer of thin sheet of aluminum coated, on the side which comes into contact with the beverage or food, with a polyethylene film or similar polymeric material.
Containers produced with such multi-layer materials are difficult to recycle due to the different chemical nature of the various layers.
The recyclability of the material forming a food or beverage container is a most important requisite both from the point of view of savings that recycling allows to be obtained and from an ecological aspect.
The possibility of having a recyclable material is a very important topic in the sector.
Containers for beverages and liquids produced of polymeric materials exist but do not offer characteristics of rigidity comparable to those of cardboard and for this reason they do not result in being suitable to produce rigid containers. The containers obtained with such materials are comprised into the category of small sacks (pouches).
The attempt to obtain containers with the necessary rigidity by using polymeric materials has failed until now.
The rigidity in the containers is in function of the thickness of the wall and more precisely varies with the cube of the wall thickness.
The use of polymeric material such as polyolefins for the production of containers having sufficient rigidity would imply a thickness which is not economical and, furthermore, is not processable due to the difficulty in folding that one encounters in the container closing phase.
Another material such as foamed polystyrene is not employable due to its fragility when it is conformed into thin layers.
Known from the patent literature (U.S. Pat. No. 5,000,991) are rigid laminates, which are used for the preparation of thermoformed containers for victuals, formed of a sheet of foamed polyester material and of a film of the same nature as the sheet, or of other polymeric material. Known from EB-A836937 are semi-rigid laminates having a thickness of 0,5 to 1.5 mm comprising a layer of polyester resin foam having a density of 0.7 to 1 g/cm
3
on which a layer having gas barrier properties, made of a polymeric material different from that of the layer in polyester foam, is adhered.
The laminates are used for the preparation by thermoformation of articles for packaging.
Materials comprising a layer in polyester foam capable of being creased to form, by folding according to the design pressed on the material, the shape of the container, are not known in patent literature.
The capability of a monoslayer or multi-layer polymeric foamed material, to be creased with a design set to develop, by folding, the shape of a coner, and the foldability of the material according to such a design, constitute indispensable requirements for the production of beverage and food containers when using the creasing and folding technique.
A material is suitable for creasing if the design pressed on it remains stable over time and if when stamping such design, breakage which could impair the possibility of folding the material does not occur.
Moreover the material must be heat-sealable so as to make possible the closure of the container.
BRIEF DESCRIPTION OF THE INVENTION
Aromatic polyester resin foamed sheets have now unexpectedly been found, which are suitable for the production of beverage and food containers, satisfying the above mentioned creasing requirements, and which present rigidity sufficient to substitute cardboard and have high impact resistance.
The sheets of the present invention are monoaxially or biaxially stretched foamed sheets, have a crysallization rate of the resin such that by heating at 120° C. for 5 minutes the crystalinity does not exceed 15% and have pressed thereon a design from which by folding a container can be developed.
DETAILED DESCRIPTION OF THE INVENTION
The polyester resin preferably used for the preparation of the stretched foamed sheets is a copolyethylene terephthalate in which from 2 to 20% in moles of units of terephthalic acid are substituted by units deriving from isophtalic and/or naphtalene-dicarboxylic acids.
Preferably, the copolyethylene terephtalate comprises from 4 to 10% of units deriving from isophtalic acid.
The intrinsic viscosity of the resin is higher than 0.8 dl/g (measured in solution 60/40 by weight of phenol and tetrachloroethone at 25° C. according to ASTM D 4603-86).
The melt strength is higher than 2 centi Newton at 280° C. preferably is from 10 to 100 centi Newton and the melt viscosity is of at least 1200 PAS at 280° C. and shear rate tending to zero, preferably 2000-20.000 PAS.
Preferably the resin is obtained by upgrading the resin having I.V. of less than about 0.7-0.75 dl/g at a temperature from 160° C. to 210° C. operating in the presence of a dianhydride of an aromatic tetracarboxylic acid, preferably pyromellitic dianhydride used in an amount of from 0.04 to 2% by weight. The preparation of the foamed sheets is carried out according to known methods. which is herewith incorporated by reference.
The melt strength and the melt viscosity are measured according to the methods hereinafter specified.
The melt strength of the resin forming the sheet shows values lower than those of the resin used for preparing the sheet.
The stretched foamed sheets of the present invention are obtained by stretching according to known methods foamed sheets having bulk density from 50 to 700 kg/m
3
, preferably 200 to 400 kg/m
3
, thickness from 0.5 to 5.
The thickness of the stretched sheets is reduced in function of the stretching ratio applied and is generally comprised from 0.2 to 3 mm, preferably from 0.6 e 1.2 mm.
The density of ie biaxially oriented sheets in general is higher than tat of the sheets prior to strething.
When the used foaming agent is a liquid hydrocarbon the density decreases.
The monoaxially stretched sheets have a density lower tan that prior to stretching (the lower density is due to the different apparatus used for the monoaxially stretching which is different from that used in the biaxially stretching).
Stretching ratio of 1.2:1 is sufficient in the case of the monoxially stretched sheets to impart the desired mechanical properties, in particular the increased impact resistance.
The high impact properties combined with the low density renders the monoaxially stretched sheets particularly suitable for the manufacture of containers for beverages and food.
The biaxially stretching (in direction of the machine and transversally) can be carried out contemporaneously or sequentially.
The stretching temperate is generally comprised from 80° C. to 120° C.
The residence time is of few seconds to 60 or more seconds.
The monoxially stretching can be conducted on a series of rolls heated at 95° C.-110° C. and rotating with different peripheral speed.
The monoaxially stretching can be conducted in the direction of the machine or transversally.
In many cases it is convenient to subject the stretched sheets to heat setting at temperatures in general comprised from 160° C. to 220° C.
The heat setting has the effect of dimensionally stabilizing the sheets (the shrinkage is remarkably reduced) and increasing the mechanical properties.
With the aim of improving the gas barrier properties of the foamed sheet, the same can be coated with a polyester resin film or other material having gas barrier properties.
In the case in which the sheet is covered with a polyester film, the barrier properties of the latter are conferred by subjecting the film to surface treatment giving it barrier properties or by the app
Al Ghatta Hussein
Cobror Sandro
Severini Tonino
Josif Albert
Modiano Guido
Nolan Sandra M.
O'Byrne Daniel
Sinco Ricerche S.p.A.
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